English: Thrust faults are low-angle reverse faults, involving upward movement of the hanging wall and downward movement of the footwall. The fault planes of thrust faults are supposed to be less than 30 degrees from the horizontal, as seen in cross-section. Thrust faults, and reverse faults in general, form by compressional stress - they are common in mountain belts.

The light-colored rocks in the upper thrust plate are part of the basal Dunham Dolostone (upper Lower Cambrian). The gray-colored rocks in the lower thrust plate are part of the Iberville Formation (Middle Ordovician). The rocks look like shales, but they're not - they're intensely calcite-veined, dark gray lime mudstones (probably argillaceous).

Normally, one would not expect older rocks above younger rocks - that's an apparent violation of the Principle of Superposition. However, the principle only applies to non-disturbed/deformed rocks.

The Champlain Thrust Fault was active during the Taconic Orogeny, an Ordovician to Silurian mountain-building event involving the collision of a volcanic island arc with Laurentia (= the North American paleocontinent). The fault zone was also active during the subsequent Acadian Orogeny (Silurian to Devonian).

Locality: lakeshore cliff in small cove north of Lone Rock Point, northwestern side of the town of Burlington, northwestern Chittenden County, northwestern Vermont, USA (44° 29' 41.33" North latitude, 73° 14' 49.46" West longitude)

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See info. at:

en.wikipedia.org/wiki/Champlain_Thrust